The present invention relates generally to a method for inactivating pathogens that may be contained in a body fluid. More specifically, the present invention relates to the inactivation of pathogens, especially in blood products, that can cause an infectious disease.
In a variety of therapies, such as transfusion and transplants, body fluids, especially blood components, such as red blood cells, platelets, plasma, leukocytes, and bone marrow, are infused from one or more individuals into a patient. Although such therapies provide treatments, some of which are life saving, and cannot otherwise be provided, due to the transmission of infectious diseases there may be potential risks to such therapies.
For example, it is known that blood can carry infectious agents such as hepatitis viruses, human immuno-deficiency viruses (an etiological agent of AIDS) and herpes virus. Although screening methods exist to identify blood that may include such viruses, blood containing viruses, and other disease causing pathogens, such as bacteria, cannot be 100% eliminated from the pool of possible blood component supplies; there is still a small chance that blood transfusions can transmit viral infection. Accordingly, a goal of biomedical research has been to reduce the risk of transmitting an infectious agent by selectively inactivating or depleting pathogens present in such blood components.
One approach has been to utilize photosensitive (photoactive) agents that when activated by light of the appropriate wavelength will destroy the ability of the pathogen to cause infection. The use of photodynamic therapy has been suggested as a way to eradicate infectious agents from collected blood and its components prior to storage and transfusion. See, Neyndorff, et al, "Development of a Model to Demonstrate Photosensitizer Mediated Viral Inactivation in Blood", Transfusion 1990:30:485-490; North et al, "Photodynamic Inactivation of Retrovirus by Benzoporphyrin Derivative: A Feline Leukemia Virus Model", Submitted to Transfusion; and Matthews et al, "Photodynamic Therapy of Viral Contaminants With Potential for Blood Bank Applications", Transfusion, 28(1), pp. 81-83 (1988).
Although effective in the destruction of the pathogen, photochemical inactivation of pathogens can also result in adverse effects on the therapeutic elements of the product, such as red blood cells or platelets. In this regard, it has been observed through immunohematology studies, that cells of blood components treated with photoactive agents which act on membranes have IgG and other plasma proteins associated with the cell membrane. IgG is an immunoglobulin plasma protein that when present is caused to bind with the cells during the photoactivation process.
Recent attempts to avoid this phenomenon have been unsuccessful. Wagner, et al., "Red Cell Surface Alterations Resulting From Virucidal Photochemical Treatment", Photochemistry & Photobiology 53:545, 1991, reports that "[u]nexpectedly, agglutination tests using rabbit anti-human IgG on [methylene blue] or [merocyanine 540] phototreated cells indicated that photosensitized red-cells have IgG associated with their surface. Plasma depletion by washing red cells prior to photo-treatment did not prevent this IgG binding upon subsequent addition of untreated autologous or AB plasma."
The presence of IgG bound to the membrane of red cells raises a host of potential concerns and difficulties in using photoinactivation drugs to inactivate pathogens in blood components. Physiological issues include reticuloendothelial system clearance of the treated red cells and complement activation. Red cells coated with IgG may be removed too quickly in a transfusion patient by the RES system.
Perhaps as important a concern with respect to IgG binding, even if the presence of IgG has no effect on cell survival or product safety, is with respect to the diagnostic implications. After treatment, the IgG bound to the cells cannot be removed from the cell membranes by washing the cells; even if extensive washings are performed. Because of the binding of the IgG to the cells, the cells exhibit a positive test result when direct antiglobulin test (DAT or Coombs') is employed.
The Coombs' test is used to detect antibody on red blood cells. The test uses rabbit antisera to immunoglobulin. When cells coated with IgG are mixed with the rabbit antisera, agglutination occurs. If IgG coated red cells are transfused into a patient, a physician loses one of his important diagnostic tests in understanding hematologic changes in the patient, since all patients receiving such a product will exhibit a positive Coombs' test.
The use of such IgG coated cells would prevent many of the currently used serological and diagnostic testing procedures. For example, red cells are typically screened using the Coombs' test. Accordingly, although the photoactive agents can result in a reduction of viable pathogens, the resulting disadvantages inherent in IgG bound red cells may outweigh the advantages.
Further, any commercially viable process for inactivating pathogens must have an activation phase that does not have an undue duration. The photoactivation phase of such photodynamic processes is dependent on the amount of photoactive agent present. However, initially the body fluid must be loaded with a sufficient amount of photoactive agent to insure that all of the pathogens bind with the agent. Therefore, excess photoactive agent could increase the activation phase of the process.